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	<h2 class="hilight">LAME - Average Bit Rate (ABR)</h2>
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<p>Suggested usage:</p>
<blockquote class="code">lame --abr 128 input.wav output.mp3</blockquote>
			
<p>
  ABR is a mix between CBR and VBR.
</p>
<p>
  Like CBR, the files will have the (approximate) bitrate specified in the
  commandline, and uses the CBR algorithm to compute the number of bits needed
  to encode each frame.<br/>
</p>

<p>
  Like VBR, the files will use different frame bitrates so instead of relying on
  bit reservoir like CBR, each frame just uses the smallest possible bitrate
  that can encode it.
</p>

<p>
	The difference between ABR and true VBR is in how the desired number of bits
	is chosen. The true VBR mode determines the number of bits based on the
	quantization noise. VBR figures out how many bits are needed so that the
	quantization noise is less than the allowed masking.
</p>

<p>
	ABR mode uses the CBR formula to determine the desired number of bits. This
	formula is based on the perceptual entropy, which is a rough measure of how
	difficult the frame is to encode.
</p>
<p>
The majority of frames in a VBR MP3 produced with an ABR method is normally at
or near the target bitrate chosen by the user, but each frame can still
potentially vary within the normal range of 8 to 320 kbps. The ABR encoder will
typically limit the range of bitrates it can choose from, or will greatly favor
certain bitrates, in an effort to ensure that the average comes out near the
target.
</p>

<h3>Who should use ABR</h3>

<p>
ABR encoding is desirable for users who want the general benefits of VBR (an
optimum bitrate from frame to frame) but with a relatively predictable file size
like they would get with constant bitrate (CBR), and a greater preference for
bitrates that are near a desired target. Inevitably, some frames will be encoded
with more bits than necessary, but the result will always be equal to or better
than that of CBR for the target bitrate.
</p>

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